It's about controlling the dangerous classes. The drug war is the perfect pretext to harass and intimidate whoever the cops feel like harassing and intimidating. I believe it was Nixon who said the drug war was a way to "target the blacks without seeming like we're targeting the blacks". Substitute poor for blacks and you have most of the drug war explained. Occasionally non-poor get caught up in the sweeps but they can almost always buy their way out. The drug war is a pretty good example of the judicial system behaving as a market. It isn't perfect but it works well enough for the wealthy. For the ruling class this is as it should be.
[WS:] I do not think I fully agree with that assessment, mainly because I do not think of the poor as a dangerous class at all. I think they are probably the least dangerous class because they are the easiest to control and have the least resources to actually threaten the elite.
I think that illegal drugs serve a somewhat different purpose - they demonize the poor turning them into savage beasts (sometimes literally sometimes figuratively) and boogey men for the middle class, whom the elite really fears. Properly frightened, the middle class toes-in the line and flock to the elite begging them for "protection" from the boogey mean. It is the same mechanism as the war on terror, or for that matter, satan and witches in the middle ages. We really have not progressed that much since the middle ages in this respect.
Wojtek